A liquid-containment vessel of a vehicle, such as a fuel tank of an aircraft, watercraft, or land vehicle, typically includes a liquid-filled lower portion containing liquid, such as fuel or other fluid, and a gas-filled headspace, such as an ullage-space, above the liquid-filled lower portion. In the context of a fuel tank, the ullage-space is typically filled with fuel vapors in addition to other gases, such as nitrogen-enriched air, to reduce the risk of an explosion via fuel vapor ignition within the ullage-space. Proper mixing of gases in the ullage-space enables maintenance of necessary inerting properties of the gases and minimizes concentrations of fuel vapors in localized areas of the fuel tank that otherwise would increase the potential for an explosion.
Injecting nitrogen-enriched or other inerting gas through injection ports of the fuel tank typically only induces limited mixing of gases in the ullage-space. On the other hand, mixing enhancement via an electric fan in the headspace would introduce a potential ignition source, apart from the additional electric energy required to drive the fan.